CK12 technical question

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PhilGood

PhilGood

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OK,

Marik, Harvey and whoever else can help me figure this out, please help me to understand something that's been bugging me about the AKG CK12 capsule. There are 3 internal "resonance" chambers. One inside each half of the backplates and then the chamber created by the seperation of the two backplates anywhere from 60 to 40 microns thick. These are supposed to be the secret of the sound in the high end, doing something 'magical' by resonating the high end.

Now follow me here.

The speed of sound at sea level is 770mph. Let's divide that up and then convert it my the shortest audible frequency.

OK.

1 mile = 5280 feet, so:

...770 miles per hour = 4065600 feet per hour (770 * 5280)
= 67760 feet per minute = 1129.33333 feet per second.

So assuming the shortest audible frequency is 20khz

1129.33333/20,000 = .056466665

1 wave of 20khz is .0565 inches in length.

.0625 is one thirty second of an inch, which is much longer than 60 microns. Yet a 20khz wave (by my calculations) is just under 1/32 of an inch (.0564). Any frequency below 20khz, the wave will be longer.

So how is it possible that a 40-60 micron chamber can effect high end frequency when the full wave won't even fit in the chamber to be reflected around. Wouldn't there be phasing problems? Is that what they were after?

I'm not saying it's not possible for these chambers to do something. What I am wondering is WHY IT WORKS, if it does. I want to understand the mechanics better.

Thanks!
 
I'm no expert on mic capsules, especially th CK12.

I'll just throw my thoughts in the mix.

A resonance chamber, no matter the size, does not need to be big enough for a full wave to propagate within it.
For example look at an average subwoofer enclosure.
A 50hz tone will resonate just fine from a 1x1x1 foot box.
So 1129.33333/50 = 22.59 ft a lot bigger than 1ft.

I think you should look more in the area of resonance chambers and loudspeaker enclosure theory to get more ideas.

The resonance of the chamber is dependent on a lot of variables, the distance between sides is a small factor (in fact for most loudspeaker enclosure calculations it's not even a variable). Other things that come into play with a resonance chamber, such as the resonant frequency of the resonators (membrains), the cubic volume of the chamber, and if the chamber is vented, or "ported" to atmosphere. Or is a sealed capsule?
I do know the chamber will need to be slim so the membrains can react with each other and be more or less coincident in space.
 
Phil,

First of all, the CK12 is a 4 plate/5 chamber design and there is nothing like a "magical resonating chamber" on high end. In short, what we deal is an acoustical labyrinth (which determines how presise is the pattern) and acoustical resistance, which determines damping (i.e. flattness of the response). The real issue is to find a presise balance between two and the whole "secret" is in tuning. In fact, since they switched from original brass ring capsules to teflon ones AKG could never do it right.

Best, M
 
Marik said:
Phil,

First of all, the CK12 is a 4 plate/5 chamber design and there is nothing like a "magical resonating chamber" on high end. In short, what we deal is an acoustical labyrinth (which determines how presise is the pattern) and acoustical resistance, which determines damping (i.e. flattness of the response). The real issue is to find a presise balance between two and the whole "secret" is in tuning. In fact, since they switched from original brass ring capsules to teflon ones AKG could never do it right.

Best, M
Click to expand...

Article written by Stephen Paul for Mix magazine:

http://mixguides.com/microphones/vintage_products/audio_vintage_microphones_part_3/


Middle of the page describes:

"In the case of the CK-12, there is a set of chambers behind the perforate surface that lies beneath the diaphragm. This is why in the photograph you can see that the pattern of holes on the outer surface is different from the round pattern found on the inner surface. In between these two walls is a chamber. This chamber has a resonance that falls within the audio range, thus creating a resonator-equipped design. It is interesting that Neumann built only aperiodic designs in its large-capsule format. Neumann did, however, make use of the resonator design in its smaller mics, notably the nickel and aluminum diaphragm types. Aperiodic designs feature elements (holes, slots, tubes, etc.) that are dimensioned in such a way that their individual resonances lie above the highest operational frequency of the capsule (also known as the boundary frequency.)

In the original AKG design, these chambers were very small, and their resonance was fairly high. It almost qualified as an aperiodic design. A production change expanded the volume of this chamber, and this brought its resonance squarely into the high-frequency range. The fascinating thing is that the change was only made to increase the overall sensitivity of the capsule and not to adjust its frequency response. The additional rise in top end was considered a negligible side effect in those days. The engineers wished to have a higher-sensitivity mic because FM broadcasting began, and with the improved specification for signal-to-noise, the mics were required to be quieter. To lessen the damping forces applied to the diaphragm, they increased the air gap behind it and enlarged the volume of the chambers. This bought them roughly a 3dB increase in sensitivity. In other words, the output of the mic for a given sound pressure rose by this amount."



I'm just trying to get a mental picture of how this works, is all.
 
Will I ever learn to clearly express what I mean! :o

Yes, I remember that part from Stephen Paul.
I don't find any special in Teflon CK12 and I am not a fan of resonator systems, and was referring to original design:

"In the original AKG design, these chambers were very small, and their resonance was fairly high. It almost qualified as an aperiodic design."

If you look carefully at the Saturn page you posted, the chamber between primary and secondary backplates is much bigger than 60um--that's where the resonator works.
In original brass ring one that chamber was much smaller.

Interesting, similar design was used in some Russian edge (and even one SD center) terminated capsules, where the internal structure was even more elaborate.

Regards, M
 
Marik said:
Will I ever learn to clearly express what I mean! :o

Yes, I remember that part from Stephen Paul.
I don't find any special in Teflon CK12 and I am not a fan of resonator systems, and was referring to original design:

"In the original AKG design, these chambers were very small, and their resonance was fairly high. It almost qualified as an aperiodic design."

If you look carefully at the Saturn page you posted, the chamber between primary and secondary backplates is much bigger than 60um--that's where the resonator works.
In original brass ring one that chamber was much smaller.

Interesting, similar design was used in some Russian edge (and even one SD center) terminated capsules, where the internal structure was even more elaborate.

Regards, M
Click to expand...

Just so I understand correctly, the teflon version does not use the same multi-chambered system, or do they just not do it properly?
 
PhilGood said:
Just so I understand correctly, the teflon version does not use the same multi-chambered system, or do they just not do it properly?
Click to expand...

Oh no, the teflon has the same 5 chamber structure. The difference is the volume of the chambers. Look again at this part of SP citation:

"A production change expanded the volume of this chamber, and this brought its resonance squarely into the high-frequency range. The fascinating thing is that the change was only made to increase the overall sensitivity of the capsule and not to adjust its frequency response. The additional rise in top end was considered a negligible side effect in those days. The engineers wished to have a higher-sensitivity mic because FM broadcasting began, and with the improved specification for signal-to-noise, the mics were required to be quieter. To lessen the damping forces applied to the diaphragm, they increased the air gap behind it and enlarged the volume of the chambers. This bought them roughly a 3dB increase in sensitivity. In other words, the output of the mic for a given sound pressure rose by this amount."
 
PhilGood said:
FWIW, here's a great page on the CK12's construction:

Here
Click to expand...
Thanks, Phil - nice link.

"You must spread some Reputation around before giving it to PhilGood again."
 
Marik said:
Oh no, the teflon has the same 5 chamber structure. The difference is the volume of the chambers. Look again at this part of SP citation:

"A production change expanded the volume of this chamber, and this brought its resonance squarely into the high-frequency range. The fascinating thing is that the change was only made to increase the overall sensitivity of the capsule and not to adjust its frequency response. The additional rise in top end was considered a negligible side effect in those days. The engineers wished to have a higher-sensitivity mic because FM broadcasting began, and with the improved specification for signal-to-noise, the mics were required to be quieter. To lessen the damping forces applied to the diaphragm, they increased the air gap behind it and enlarged the volume of the chambers. This bought them roughly a 3dB increase in sensitivity. In other words, the output of the mic for a given sound pressure rose by this amount."
Click to expand...

You would think AKG would take note of the popularity of the original and begin manufacturing a new capsule based on the old specs.

I wonder if the mechanical patent on this has expired. :cool:
 
I don't claim to know much about the CK12 capsule, but the bottom of the audio spectrom is 20-40 *hz*, not *khz*. This might affect calculations by a factor of 1000.-Richie
 
Richard Monroe said:
I don't claim to know much about the CK12 capsule, but the bottom of the audio spectrom is 20-40 *hz*, not *khz*. This might affect calculations by a factor of 1000.-Richie
Click to expand...

I was using 20khz because it is the shortest of waves in the audible spectrum. Anything below that would be a longer wave. 20hz would be muuuuuuch longer.
 
Phil,
I build this capsule. You won't find anyone who will explain the precise technical workings of a CK12.

To make a long story short, a membrane by itself can easily reproduce all audible frequencies (and many inaudible). Dampning within the capsule determines which frequencies it will pass to the amplifier.
 
Tim, I have no doubts that if anyone truly understands the design and inner workings of this capsule, it's you.

I look forward to seeing what your capsule sounds like.

I am awaiting it with great anticipation and know I will be satisfied!;)
 
P.S. Tim, I'm glad you posted here. Your insights will be very valuable indeed!

Someone who is brave enough to take on making a modern version of this with the care you take is someone to be admired in any book!

(Yes, I'm the Phil who ordered that capsule from you last week.)
 
Last edited:
Thanks for the interesting discussion Phil!! :D

I find it interesting that we can put a man on the moon, and fire lazers 1000 miles and blow out the tires on a vehicle without damaging the vehicle, and even make viagra, but we can't recreate a 50 year old capsule design.

LOL

Funny stuff. Anyone that can accurately capture it will undoubtably make a lot of $$$....... Is that Tim???
 
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